This invention relates to a process for increasing the frylife of edible oil. The process involves heating the oil at very high temperature under vacuum for a short time while stripping the oil with steam or inert gas to remove components from the class of tocopherols, tocotrienols, sterols (preferably cholesterol), trace pesticides and other trace quinone-type structures, herein described as materials deleterious to frylife.
In order to build superior taste into edible oil products, they must undergo certain processing steps. The most important, from a finished flavor standpoint, is deodorization. Deodorization is a moderately high temperature vacuum steam distillation process used to remove volatile odoriferous compounds from edible fats and oils. These odoriferous compounds are more volatile than the fats and oils, so they can be separated by use of a stripping agent such as steam. High temperature and low pressure increase the relative volatility of these compounds. Since the senses of taste and smell are closely linked, deodorization improves the flavor of the product as well as the odor. The finished product is ideally a bland oil.
The earliest used fats and oils did not require deodorization. Animal fat or lard in its natural form has a desirable taste and odor. Olive oil also has a very agreeable flavor. However, in later years other vegetable oils came into use which had such poor flavor and odor that they were inedible without further processing. In particular, as the cotton industry developed in the United States, there was incentive to use cottonseed oil for edible purposes. The processes of alkali refining and hydrogenation also imparted off-flavors and odors to the oils. Hence, there was a need for the development of deodorization processes to create desirably bland fats and oils.
Deodorization was first practiced by blowing steam through a batch of heated oil. This process significantly improved the odor and flavor of the oil. The next major step was steam stripping used in combination with a vacuum. Use of a vacuum not only enhanced the separation of the volatile odoriferous materials, but it also helped to prevent oxidation of the fats and oils at the high deodorization temperatures. There were many advances in equipment design. Semicontinuous and continuous deodorizers were later developed which enabled the more efficient deodorization of large amounts of fats and oils.
The theoretical aspects of steam stripping are governed by Raoult's law and Dalton's law. T. Applewhite, Bailey's Industrial Oil and Fat Products, 1st Ed., Vol. 3, pp. 129-137 John Wiley & Sons, New York (1985) outlines the mathematical relationships involved in deodorization and the influence of different operating variables.
As discussed above, deodorization is more accurately described as a moderately high temperature vacuum steam distillation or steam stripping process, but it was originally called deodorization because of its removal of undesirable odors and flavors. However, the process of this invention amounts to more than simply deodorization, because it is primarily concerned with increasing oil frylife by removing the aforementioned components deleterious to frylife using extreme stripping conditions, while minimizing undesirable thermally induced side reactions. Oil frylife is the amount of time an oil can be used to fry food.
Previous deodorization have not addressed oil frylife. For example, U.S. Pat. No. 2,621,196 to Thurman, issued Dec. 9, 1952, discloses a process for deodorizing edible glyceride oils in which oil is subjected to steam distillation in a plurality of increasing temperatures, starting at a temperature between 395.degree. F. and 450.degree. F. and ending with a temperature between 500.degree. F. and 600.degree. F. Thurman does not discuss frylife. While the final stage temperature of the Thurman process is relatively high, the total deodorization time is more than 1 hour. This is in contrast to the short time of the instant invention.
U.S. Pat. No. 3,933,953 to Leva, issued Jan. 20, 1976, discloses an apparatus and method for stripping fatty acids and removing objectionable odors and flavors from oils and fats. The apparatus is a chamber which encloses a stack of horizontal, parallel disposed plates, each plate having a plurality of apertures defined by chimneys and extending downwardly from the plates. Leva states that the upper limit of temperature for conducting the deodorization is below 575.degree. F. (302.degree. C.) to 600.degree. F. (316.degree. C.). The purpose of the Leva process is to remove fatty acids instead of the materials deleterious to frylife removed in the process of the instant invention. These deleterious materials are much less volatile than fatty acids, so more rigorous processing conditions are needed.
One approach to improving frylife is described in U.S. Pat. No. 3,619,213 to Haynes et al., issued May 22, 1969. A minor proportion of a particular silicon-containing additive is added to a frying fat composition to retard darkening in the frying fat over long periods of frying use. Pyrogenic silica at a 0.05 to 0.7 weight percentage level is a preferred anti-darkening additive.
It is an object of the present invention to provide a process that increases the useful frylife of edible oil without damaging the oil or using additives.
It is another object of this invention to increase the oil's frylife by subjecting it to a process in which dramatic stripping is achieved by heating the oil under vacuum to a very high temperature and held at that temperature for a short period of time, while it is stripped with steam or inert gas.
These and other objects of the invention will become clear from the disclosure herein.
All percentages are by weight unless otherwise defined.